This invention relates generally to weather forecasting and more particularly to forecasting geostrophic wind velocity associated with wave cyclones.
Forecasting weather, in some cases, is an art. Many forecasting techniques have developed, however, to assist a meteorologist in accurately forecasting the weather. Some of the forecasting techniques are based on a theoretical model of the earth using a noninertial frame of reference. The noninertial frame of reference permits an analysis of a unit of mass being acted on by various forces to produce changes in the weather.
An analysis using the noninertial frame of reference leads to the well known geostrophic wind equations, as described in "Introduction to Theoretical Meteorology," by Seymour Hess (1959), pp. 161-178. The geostrophic wind equations relate the derivative of pressure P relative to distance x, i.e., .delta.P/.delta.x, to a resulting geostrophic wind velocity VG according to the following simplified equation: EQU VG=[1/(D.times.F)].times.(.delta.P/.delta.x), (1)
where D is equal to the atmospheric density and F is equal to the Coriolis parameter.
Meteorologists use the geostrophic wind equation to forecast the wind velocity associated with a particular pressure surface. In the simplest case, two pressure sensors separated by a known distance .DELTA.x monitor the atmospheric pressure at their respective locations. The pressure detected at each location is then subtracted to produce a change in pressure .DELTA.P, which is an approximation of the actual derivative .delta.P/.delta.x. The change in pressure .DELTA.P is then divided by the known distance .DELTA.x between the sensors to produce the change in pressure over the change in distance, i.e., .DELTA.P/.DELTA.x, which is approximately equal to .delta.P/.delta.x.
The atmospheric density D is then computed according to the following known equation: EQU D=P/(R.times.T), (2)
where R is equal to the Universal Gas Constant and has a value of 287.05 J/(Kg.times..degree.K.); P is equal to the current pressure; and T is equal to the current temperature in degrees Kelvin. The Coriolis parameter can also be computed as a function of latitude according to the following known formula: EQU F=2.times..OMEGA..times.sin(.phi.), (3)
where .OMEGA. is equal to the earth's angular velocity in radians per second; and .phi. is equal to the latitude of the pressure sensor location measured in degrees.
Once all of the variables of the geostrophic wind equation are known, the geostrophic wind velocity can be computed according to the geostrophic wind equation (1). The velocity produced by the geostrophic wind equation provides from three to twelve hours of advance warning depending on the geographic position of the sensors. On average, measurements performed in the Midwest United States, for example, produce approximately three hours of advance warning, whereas in the Western United States the advance warning is approximately twelve hours.
The above-described method requires a relatively high degree of understanding and mathematical ability. Although meteorologists possess this level of sophistication, the average consumer does not. In addition, the above-described method requires at least two pressure sensors as well as a means to communicate with both of the sensors. Meteorological services can provide the pressure readings at given locations; however, this method requires a means for down-loading the pressure data and means for converting the pressure readings to geostrophic wind velocity. As a result of the complexity of either technique, geostrophic wind forecasters are relegated to the offices of meteorologists, rather than the consuming public.
Another technique which requires only a single pressure sensor uses historical data to predict future wind velocity. U.S. Pat. No. 4,631,960 issued to Wogerbauer describes an electronic recording manometer having wind velocity prediction. The Wogerbauer apparatus senses change in pressure over time with the use of a pressure sensor under microprocessor control. Historical data relating change in pressure over time to wind velocity is stored in memory. Although little discussion is made of the historical data in Wogerbauer, presumably the historical wind velocity is an average wind velocity over a given period of time as measured at the current location of the apparatus. For each detected change in pressure over time, a corresponding historical wind velocity can then be fetched from memory and displayed on an LCD display.
The Wogerbauer apparatus suffers from several disadvantages. The first is the reduced accuracy of the wind velocity prediction. The accuracy of the historical data is limited by the length of the historical period over which the historical data is captured. Also, past wind patterns are not a perfect indicator of future wind patterns.
The second disadvantage of the Wogerbauer apparatus is its complexity. The historical wind velocity data is based on a particular geographical location. Thus, the historical wind velocity must be separately compiled for all geographical areas in which the apparatus operates. Therefore, either separate devices must be manufactured for different regions or the memory made large enough to store the historical data for all regions and allow the user to select the appropriate one. As a result of these and other disadvantages of the Wogerbauer apparatus, historical wind velocity forecasters are not widely in use by the public.
Accordingly, a need remains for a geostrophic wind forecasting apparatus which accurately and inexpensively forecasts geostrophic wind.